296
��Popular Science Monthly
��stead of the condenser across the inter- rupter, the former custom. The battery is a small case containing ten, eight am- pere-hour cells of twenty volts, and the secondary is connected with the dis- charge electrode or oscillator mounted on top of a small case within which the
���Fig. 2. The apparatus in detail. It weighs, complete, about 30 lbs, for 150 watts, and includes one self-exciting 250 cycle generator with synchronized spark gap, one Dubilier condenser, one transformer in oil, and a loose coupled tuning coil
rest of the apparatus is fastened. The os- cillator is mounted outside to take advan- tage of the rush of air in the aeroplane track along, thus cooling it. The aerial and equivalent capacity is connected di- rectly across the spark gap, thus elimin- ating the necessity of tuning by means of a condenser and tuning coil. The arrangement is much the same as that which Hertz and Marconi used in their initial experiments. It will be seen, therefore, that the operating circuit pro- duces a natural wave without the neces- sity of adjustments such as are necessary for most spark transmitters.
The primary input is about twenty volts and one-half an ampere. The inter- rupter produces a musical note of about 250 frequencies. The trailing wire, which is used as the aerial, is about 150 feet long, and has a three-pound lead weight attached to it. With this small power we were able to obtain five-tenths of an ampere in the aerial wire circuit. the capacity of which was al^out 0.00003 m.f. It was found that communication could be efifected a distance of fifteen miles. This served the purpose very well, especially for directing artillery
��fire. The receiving wireless station was situated about one mile behind the guns. Between the receiving station and the gunners a regular telephone line was set up.
The position of the aviator is obvi- ously very perilous. He must be right over the enemy's trenches if he is to direct every shot of the artillery. When a shot falls short or long or too much to the right or to the left, he flashes the information at once to his station. The next shot follows the course that he in- dicates. This is the most effective elec- trical work which has been done in the Avar.
The aeroplane employed in this dan- gerous service is a two-seater contain- ing a pilot and the observer. The ob- server sends his messages as quickly as he makes his observations.
Another set of instruments is used, of 150 watts capacity, the energy being ob- tained from a generator driven by the engine of the aeroplane. Various in- stallations are used of this capacity, some utilizing direct current and some
���Fig. 3. The apparatus with a small engine for portable use
alternating current. The best instru- ment in my opinion is one which has a 250 cycle alternator attached by a belt to the gas engine. This generator is of remarkably light weight and is so con- structed that it is self-exciting. The whole installation, including the genera- tor, a closed core transformer in oil, a key, condensers, loose-coupled tuning coils and hot wire meter weighs com- plete but 27 pounds. How remarkable is this installation may be gathered from the fact that the ordinary machine
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